Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium. The polishing slurry is typically used in conjunction with a polishing pad (e.g., polishing cloth or disk). Suitable polishing pads are described in U.S. Pat. Nos. 6,062,968, 6,117,000, and 6,126,532, which disclose the use of sintered polyurethane polishing pads having an open-celled porous network, and U.S. Pat. No. 5,489,233, which discloses the use of solid polishing pads having a surface texture or pattern. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
Polishing compositions for silicon-based inter-metal dielectric layers have been particularly well developed in the semiconductor industry, and the chemical and mechanical nature of polishing and wear of the silicon-based dielectrics is reasonably well understood. One problem with the silicon-based dielectric materials, however, is that their dielectric constant is relatively high, being approximately 3.9 or higher, depending on factors such as residual moisture content. As a result, the capacitance between the conductive layers is also relatively high, which in turn limits the speed (frequency) at which the circuit can operate. Strategies being developed to reduce the capacitance include (1) incorporating metals with lower resistivity values (e.g., copper), and (2) providing electrical isolation with insulating materials having lower dielectric constants relative to silicon dioxide. Such low dielectric constant materials typically include organic polymer materials, inorganic and organic porous dielectric materials, and blended or composite organic and inorganic materials, which can be porous or non-porous. It would be highly desirable to incorporate low dielectric constant materials into semiconductor structures while still being able to utilize the conventional chemical-mechanical polishing (CMP) systems for polishing the surface of the resulting dielectric material during the semiconductor wafer processing.
Several chemical-mechanical polishing compositions for substrates containing low dielectric constant materials are known. For example, U.S. Pat. No. 6,043,155 discloses a cerium oxide-based slurry for inorganic and organic insulating films. U.S. Pat. No. 6,046,112 discloses a polishing composition for polishing low dielectric materials comprising zirconia abrasive and either tetramethylammonium hydroxide or tetrabutylammonium hydroxide. U.S. Pat. No. 6,270,395 discloses a polishing composition for low dielectric materials comprising abrasive and an oxidizing agent.
Surfactants are commonly used in chemical-mechanical polishing compositions to function as dispersants or flocculating agents. For example, U.S. Pat. No. 6,270,393 discloses an abrasive slurry comprising alumina, an inorganic salt, a water-soluble chelating agent, and a surfactant which purportedly acts as a dispersant for the abrasive. U.S. Pat. No. 6,313,039 discloses a polishing composition comprising an abrasive, an hydroxylamine compound, an oxidizing agent, and optionally a surfactant that purportedly alters the surface charge on the substrate being polished. U.S. Pat. No. 6,348,076 discloses polishing compositions for metal layer CMP comprising surfactants, in particular anionic surfactants. U.S. Published Patent Application 2001/0005009 A1 discloses polishing compositions comprising surfactants, including anionic, cationic, ampholytic, and nonionic surfactants, to act as dispersing agents. U.S. Published Patent Application 2001/0008828 A1 discloses an aqueous polishing composition for copper and barrier film polishing comprising an abrasive, an organic acid, a heterocyclic compound, an oxidizer, and optionally a surfactant. U.S. Published Patent Application 2001/0013507 A1 discloses a method of polishing low dielectric constant inorganic polymer layers comprising zironica abrasive and a nonionic, anionic, cationic, or amphoteric surfactant, which purportedly acts to stabilize the polishing slurry against settling, flocculation, and decomposition. WO 01/32794 A1 discloses a tantalum barrier slurry for CMP comprising an organic additive, which can be any of a variety of surfactants, that purportedly forms bonds with the surface of the silica or copper substrate and suppresses formation of silica precipitates and copper staining. EP 810 302 B1 discloses a polishing composition comprising a sorbitan fatty acid ester and a polyoxyethylene derivative of a sorbitan fatty acid ester as corrosion inhibitors. EP 1 088 869 A1 discloses an aqueous dispersion for CMP comprising abrasive particles and an amphipathic surfactant having an HLB value of 6 or lower. EP 1 148 538 A1 discloses a polishing composition comprising cerium oxide abrasive and a surfactant (e.g., anionic, nonionic, cationic, or amphoteric) that purportedly acts as a dispersant.
Though the use of surfactants in chemical-mechanical polishing compositions is well known, none of the prior art references recognizes the particular benefits of nonionic surfactants as compared to other types of surfactants, such as anionic, cationic, and amphoteric surfactants. It has been found that nonionic surfactants can provide improved selectivity in substrate layer removal rates. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.